1. Field of the Invention
This invention relates to a refrigerant compressor which uses 1,1,1,2-tetrafluoroethane (to be referred to as R134a hereinafter) which is an HFC type refrigerant or a mixture of HFC type refrigerants (such as a mixture of R134a, R32 and R125, a mixture of R134a, R143a and R125 or a mixture of R32 and R125) as a refrigerant and a refrigerator oil having compatibility with the refrigerant and to a cooling apparatus.
2. Background Art
Most refrigerant compressors for refrigerators, automatic vending machines and show cases have conventionally used dichlorodifluoromethane (to be referred to as R12 hereinafter) as a refrigerant. This R12 falls under flon regulations because of the disruption of the ozone layer. R134a is now being studied for use in refrigerators as a substitute for this R12 (refer to Laid-open Japanese Patent Application No. Hei 1-271491, for example).
Although chlorodifluoromethane (R22) has been used in air conditioners and the like, much attention is paid to HFC type mixed refrigerants from a viewpoint of environmental preservation.
However, HFC type refrigerants such as the above-described R134a have poor compatibility with a refrigerator oil such as mineral oil or alkylbenzene oil which is currently used and cause a failure in lubricating the compressor due to the bad returning of the oil to the compressor and the absorption of the separated refrigerant at the time of activation.
Therefore, the inventors of the present invention have studied a polyol ester type oil as a refrigerator oil which has compatibility with HFC type refrigerants such as R134a. However, when this polyol ester type oil is used in a rotary type compressor, a fatty acid produced by the hydrolysis of the oil caused by heat corrodes sliding members and causes wear. Powders produced by this wear exert a bad influence on organic materials such as magnet wires of electric elements of the compressor and thus impair the durability of the compressor.
The inventors have conducted studies to use a combination of an HFC type refrigerant as a refrigerant and a polyol ester type oil as a refrigerator oil in a rotary type compressor and have found that a carboxylic acid which is produced by the hydrolysis of the polyol ester type oil for lubricating sliding members caused by the frictional heat of the sliding members of the rotary type compressor corrodes iron type materials or reacts with iron type materials to become metal soap or sludge, thereby reducing refrigerating capacity.
As a result, the inventors have found that the thermal cracking of the polyol ester type oil caused by frictional heat generated by the sliding members can be suppressed by a combination of a specific polyol ester type oil, a specific additive and a specific sliding material (refer to Laid-open Japanese Patent Application No. Hei 6-295357).
However, according to the above technique, it is necessary to strictly control the production process, that is, the concentrations of water, chlorine and oxygen, in order to suppress hydrolysis when the polyol ester type oil is used. Therefore, the above invention has a problem that control is troublesome.